ADSORPTION FROM BINARY-SOLUTIONS ON SILANIZED SILICA-GEL

The adsorption process of polar substances from binary mixtures with benzene and n-heptane on nonmodified and chemically modified silica gels was compared. Liquid chromatography column packings, based on silica gel, with bonded dimethyl or octyl groups were used as the modified adsorbents. The excess adsorption isotherms were measured under static conditions. The capacity of the surface layers was calculated by using the Dubinin-Radushkevich type of adsorption isotherm equation. It was found that the capacity of the surface layer of silanized silica gel for the same mixture is about half the capacity of a nonmodified silica gel. The hydroxyl groups and methyl or octyl groups of the surface interact with polar and nonpolar segments of the adsorbate molecules, respectively. This causes a specific orientation of the molecules on silanized silica gel which is different from that on the fully hydroxylated silica gel. The correlation of the extent of adsorption from the liquid phase and the concentration of the polar and nonpolar species on the silica gel surface is discussed. © 1990.